The invention relates to a base station for a digital time division multiple access radio network, the base station comprising a radio transceiver, means for measuring a time difference between the transmissions of the transceiver and a mobile radio station due to a distance between the base station and the mobile radio station, and means for controlling the mobile radio station to adjust its transmission relative to the transmission of the transceiver by a predetermined timing advance compensating for said time difference, said timing advance having a maximum value determining a maximum radius r.sub.max for an effective service area of the base station transceiver.
In digital Time Division Multiple Access (TDMA) radio systems, a plurality of mobile radio stations may utilize the same radio channel on a time division basis for communication with the base station. Communication on the radio channel takes place in a number of successive time slots, e.g. 8 time slots, allocated to the users as required. A mobile radio station is synchronized with a signal from the base station, and it transmits in accordance with this sync so that the signal from the mobile station is received at the base station in a time slot allocated for this particular mobile station. Mobile stations, however, may be located at different distances from the base station, whereby the propagation delay caused by this distance has to be taken into account in the synchronization of the timing of transmission of each mobile station with the base station so that the signal will be received at the base station in the right time slot. For this purpose, the base station measures the time difference between its own transmission and the transmission received from the mobile station, on the basis of which it defines a suitable timing advance for the mobile station. The mobile station uses this timing advance to advance the timing of its transmission relative to a basic time instant defined by the sync received from the base station. Various intrasystem features limit the timing advance to a certain maximum. This maximum of the timing advance, in turn, dictates the maximum cell size that the base station of the system is able to serve. In the Pan-European mobile radio system GSM (Global System for Mobile Communication), for instance, the timing advance may vary in the range between 0 and 233 .mu.s, which means a cell size with a maximum radius of 35 km. However, such a cell size of 35 km may be too small e.g. in sparsely populated areas with a low traffic load. Due to the above-mentioned limitation, however, increasing the cell size has not been possible even though the capacity of the base station and the topology of the terrain would otherwise have allowed larger cells.